Paper feeding device for image forming apparatus

ABSTRACT

A paper feeding device for an image forming apparatus includes a pick-up roller for picking up paper from a paper feeding cassette and for feeding the paper to a registration roller. The registration roller registers a leading end of a sheet of paper and compensates for skew of the paper by stopping to allow the leading end of the paper to contact the registration roller to form a paper curl and maintaining the paper curl. The paper feeding device does not require a feeding roller but instead controls the rotation of the pick-up roller to form the paper curl. Therefore, the paper feeding device is compact and can be used with a compact image forming apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(a) of Korean Patent Application No. 2005-55395, filed on Jun. 25, 2005, and Korean Patent Application No. 2005-97852 filed on Oct. 18, 2005, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus, such as a printer, a copier, or a multi-functional device. More particularly, the present invention relates to a paper feeding device for an image forming apparatus.

2. Description of the Related Art

As known to those skilled in the art, an image forming apparatus has a paper feeding device which supplies papers stacked in a paper feeding cassette into a printing portion of the image forming apparatus. The paper feeding device comprises a pick-up roller, a registration roller, and a feeding roller. The pick-up roller separates the paper in the paper feeding cassette into individual sheets and supplies the sheets of paper to the feeding roller. The registration roller registers a leading end of a sheet of paper and compensates for skew of the paper. The feeding roller feeds the paper to the registration roller and forms and maintains a curl to register the leading end of a sheet of paper and compensate for skew of the paper.

FIG. 1 is a schematic view of a conventional paper feeding device in a typical image forming apparatus. A pick-up roller 10 is formed above a paper feeding cassette (not shown) to pick up sheets of paper P which are stacked in the paper feeding cassette. The pick-up roller 10 includes a paper contact portion 11 which has an arc-shaped cross section.

The pick-up roller 10 generates less paper dust than a cylindrical pick-up roller and can reduce the load on the registration roller while paper is supplied.

A feeding roller 20 is disposed between the pick-up roller 10 and a registration roller 30 to feed the paper P to the registration roller 30. Additionally, the feeding roller 20 forms and maintains a paper curl C of the paper P to register the leading end of the paper P and compensate for skew of the paper.

The registration roller 30 feeds the paper after registering the leading end of the paper and compensating for skew of the paper. To this end, the registration roller 30 stops until a paper curl is formed between the registration roller 30 and the feeding roller 20 and, then, after a certain time, rotates to feed the paper.

In particular, the leading end of every sheet of paper P fed from the paper feeding cassette by the pick-up roller 10 passes the feeding roller 20 and arrives at the registration roller 30. Since the registration roller 30 is stopped, the leading end of the paper does not pass the registration roller 30 but forms a paper curl C. At this time, the paper is subjected to a force in an opposite direction of the forwarding of the paper by the paper curl C, but the feeding roller 20 holds the paper to maintain the curl C. By this operation, the paper feeding device registers the leading end of the paper and compensate for skew of the paper.

This type of conventional paper feeding device requires a feeding roller 20 to form the paper curl C to register the leading end of a sheet of paper and compensate for skew of the paper. The feeding device therefore requires significant space in the image forming apparatus, and, it is difficult to use the feeding device in a compact image forming apparatus.

Accordingly, there is a need for an improved paper feeding device which is more compact than conventional paper feeding devices.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a paper feeding device of an image forming apparatus which can be easily used in a compact image forming apparatus.

Another aspect of the present invention is to provide a paper feeding device for an image forming apparatus which can increase the stability and precision of paper feeding operations.

In accordance with an aspect of the present invention, a paper feeding device for an image forming apparatus comprises a pick-up roller, a registration roller, and a driving unit. The pick-up roller has a paper contact portion with an arc-shaped cross section. The registration roller registers a leading end of a sheet of paper fed by the pick-up roller and compensates for skew of the paper. The driving unit drives the pick-up roller between a first position for preparing to pick-up a sheet of paper and a second position for forming a paper curl.

The device may further comprise a pick-up gear engaged with a pick-up roller shaft. The pick-up gear is stopped from rotating at each of the first and the second positions by a solenoid.

The pick-up gear may comprise a first and a second locking portions corresponding to each of the first and the second positions. A movable body of the solenoid is locked in the first and the second locking portions so that the pick-up gear is stopped at the first and the second positions, respectively.

A rotational distance of the pick-up roller may be set to meet the following equation: 1+α≦L<LE in which, L is the distance the pick-up roller rotates from a reference position (S1) where the paper contact portion of the pick-up roller starts to contact the paper to the second stop position (S2), 1 is a distance between the reference position (S1) and the registration roller, α is an amount of paper curl, and LE is a distance between the reference position (S1) and the first stop position (S3).

The device may further comprise a bottom tray that elastically presses the paper into contact with the pick-up roller, and a means for preventing a reverse moment which is generated at the pick-up roller by the bottom tray.

The means for preventing the reverse moment may comprise a pick-up cam rotating coaxially with the pick-up roller to move the bottom tray upwardly and downwardly, and a cam stopper pressing the pick-up cam to prevent the reverse moment generated by the bottom tray.

The pick-up cam may comprise a locking recess in which a leading end of the cam stopper is locked.

Each of the first and the second locking portions may comprise a locking protrusion at one side, and a guide contour at the other side.

In accordance with another aspect of the present invention, a paper feeding device for an image forming apparatus comprising a registration roller for registering a leading end of a sheet of paper and compensating for skew of the paper, and a pick-up roller for picking up a sheet of paper to feed to the registration roller and, as the leading end of the paper contacts the registration roller to form a paper curl, stopping to maintain the paper curl.

The device may further comprise a solenoid controlling the rotation of the pick-up roller to stop the pick-up roller at a first position for preparing to pick-up a sheet of paper and at a second position for forming a paper curl.

The device may further comprise a pick-up roller shaft rotatably supporting the pick-up roller and a pick-up gear engaged with the pick-up roller shaft to rotate the pick-up roller. The pick-up gear may comprise a first and a second locking portions corresponding to the first and the second positions, and the solenoid may comprise a movable body which may be locked in the first and the second locking portions so that the pick-up gear is stopped at the first and the second positions, respectively.

Each of the first and the second locking portions may comprise a locking protrusion at one side, and a guide contour at the other side.

The rotational distance of the pick-up roller may be set to meet the following equation: 1+αL<LE

in which, L is the distance the pick-up roller rotates from a reference position (S1) where the paper contact portion of the pick-up roller starts to contact the paper to the second stop position (S2), 1 is a distance between the reference position (S1) and the registration roller, α is an amount of paper curl, and LE is a distance between the reference position (S1) and the first stop position (S3).

The device may further comprise a bottom tray for pressing the paper into contact with the pick-up roller and means for preventing a reverse moment which is generated at the pick-up roller by the bottom tray.

The means for preventing the reverse moment may comprise a pick-up cam rotating coaxially with the pick-up roller to move the bottom tray upwardly and downwardly, and a cam stopper pressing the pick-up cam to prevent the reverse moment generated by the bottom tray.

The pick-up cam may comprise a locking recess in which a leading end of the cam stopper is locked.

In accordance with still another aspect of the present invention, a paper feeding device for an image forming apparatus comprises a registration roller for registering a leading end of a sheet of paper, a rotatable pick-up roller for picking up a sheet of paper from a stack of paper and feeding the sheet of paper to the registration roller, the pick-up roller having a paper contact portion, and means for rotating the pick-up roller and stopping the pick-up roller at a first stop position and a second stop position. The first stop position and the second stop position are arranged to meet the following equation: 1+α≦<L<LE

in which, L is the distance the pick-up roller rotates from a reference position (S1) where the paper contact portion of the pick-up roller starts to contact the paper to the second stop position (S2), 1 is a distance between the reference position (S1) and the registration roller, α is an amount of paper curl, and LE is a distance between the reference position (S1) and the first stop position (S3).

The means for rotating and stopping the pick-up roller may comprise a rotatable pick-up roller gear engaging the pick-up roller and means for engaging the pick-up roller gear to prevent the pick-up roller gear from rotating.. The pick-up roller gear is driven to rotate the pick-up roller, and the pick-up roller gear has first and second locking portions. The means for engaging the pickup roller engages the first and second locking portions of the pick-up roller gear to prevent the pick-up roller gear from rotating.

The means for engaging the first and second locking portions of the pick-up roller gear may comprise a solenoid engaging the pickup gear.

The pick-up roller gear may be driven by an input gear, and the pick-up roller gear may have a toothed portion where the pick-up roller gear is engaged with the input gear, and first and second cut-off portions where the pick-up roller gear is not engaged with the input gear. The first and second cut-off portions correspond to the first and second stop positions.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view of a conventional paper feeding device of a typical image forming apparatus;

FIGS. 2A and 2B are schematic views of a paper feeding device according to an exemplary embodiment of the present invention, with a pick-up roller positioned at a first position;

FIGS. 3A and 3B are schematic views of a paper feeding device according to an exemplary embodiment of the present invention, with a pick-up roller positioned at a second position;

FIG. 4 is a perspective view of a paper feeding device of an image forming apparatus according to an exemplary embodiment of the present invention;

FIGS. 5A and 5B are views illustrating the operation of a paper feeding device according to an exemplary embodiment of the present invention, taken along the line V-V of FIG. 4: FIG. 5A shows a pick-up roller positioned at a first position, and FIG. 5B shows when a pick-up roller positioned at a second position; and

FIGS. 6A and 6B are views illustrating the operation of a paper feeding device according to an exemplary embodiment of the present invention, taken along a line VI-VI of FIG. 4: FIG. 6A shows a pick-up roller positioned a first position, and FIG. 6B shows a pick-up roller positioned at a second position.

Throughout the drawings, the same reference numerals will be understood to refer to the same elements, features, and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

FIGS. 2A through 3B are views of a paper feeding device of an image forming apparatus according to an exemplary embodiment of the present invention. As shown, the paper feeding device of an image forming apparatus according to an exemplary embodiment of the present invention comprises a pick-up roller 100, a registration roller 200, and a driving unit (350). As shown in FIG. 4, the driving unit (350) comprises a solenoid 300 and a pick-up gear 120.

The pick-up roller 100 is rotatably disposed by a paper feeding cassette (not shown) and includes a paper contact portion 101 which has an arc-shaped cross section. A paper guide 130 is positioned opposite to the pick-up roller 100. The pick-up roller 100 rotates to separate the uppermost sheet of paper from the stack of paper P and feed the individual sheet of paper to the registration roller 200.

The pick-up roller 100 according to an exemplary embodiment of the present invention stops at first and second positions. Since the pick-up roller 100 stops at two positions, the paper feeding device according to an exemplary embodiment of the present invention does not require a separate feeding roller to form a paper curl C to register a leading end of a sheet of paper and compensate for skew of the paper. Therefore, the paper feeding device and the image forming apparatus can have a simpler and more compact construction in comparison with conventional paper feeding devices. As will be explained in detail below, the rotation of the pick-up roller 100 may be stopped at two positions by the use of the solenoid 300 and a control unit (not shown).

As shown in FIGS. 2A and 3A, a first position S3 is a first stop position for preparing to pick-up a sheet of paper P by the pick-up roller 100, a second position S2 is a second stop position for forming and maintaining a paper curl C by co-operation of the pick-up roller 100 and the registration roller 200, and a reference position S1 is a position where the paper contact portion 101 of the pick-up roller 100 starts to contact the paper P.

More particularly, when the leading end of the picked up paper P contacts the stopped registration roller 200 and does not pass the registration roller 200, the pick-up roller 100 rotates to move to the second position S2 so that a paper curl C can be formed by a feeding force of the pick-up roller 100.

In an exemplary embodiment, the rotational distance of the pick-up roller 100 is set to meet the following equation: 1+α≦L<LE

in which, L is the distance the pick-up roller rotates from a reference position (S1) where the paper contact portion of the pick-up roller starts to contact the paper to the second stop position (S2), 1 is a distance between the reference position (S1) and the registration roller, α is an amount of paper curl, and LE is a distance between the reference position (S1) and the first stop position (S3).

A pick-up gear 120 is formed at an end portion of one side of a pick-up roller shaft 110. As shown in FIGS. 6A and 6B, the pick-up gear 120 is meshed with an input gear 170 that is connected through a driving force transmission device (not shown) such as a gear train with a driving source (not shown) such as a driving motor.

The pick-up gear 120 comprises a toothed portion 124, and first and second cut off portions 125, 126. The toothed portion 124 meshes with the input gear 170, and each of the cut off portions 125, 126 cuts off the meshed connection between the input gear 170 and the pick-up gear 120 when the pick-up roller 100 stops at the first and the second positions S3, S2.

First and second locking portions 121, 122 are formed at one side of the pick-up gear 120. A movable body 320 of the solenoid 300 is locked in each of the first and the second locking portions 121, 122 so that the pick-up gear 120 and the pick-up roller 100 stop at the first position and the second position, respectively.

Preferably, each of the locking portions 121, 122 comprises locking protrusions 121 a, 122 a at one side, and guide contours 121 b, 122 b at the other side.

The registration roller 200 compensates for skew and registers the leading end of a sheet of paper P fed by the pick-up roller 100, and is provided downstream of the pick-up roller 100. Additionally, in cooperation with the pick-up roller 100, the registration roller 200 allows the paper P to form a paper curl C so that the paper P can be fed with a registered leading end and with compensated skew.

As shown in FIGS. 6A and 6B, the solenoid 300 comprises an electromagnet 310, a movable body 320, and a spring member 330. If the power supply is cut to the solenoid 300, the movable body 320 is swung by the spring member 330 so that the free end portion is moved out of the electromagnet 310. Under this circumstance, the free end portion of the movable body 320 is sequentially locked into the locking protrusions 121 a, 122 a of the first and the second locking portions 121, 122 while being guided along the guide contours 121 b, 122 b of the first and the second locking portions 121, 122. As the leading end of the movable body 320 is locked in the locking protrusions 121 a, 122 a of the first and the second locking portions 121, 122, the pick-up gear 120 and the pick-up roller shaft 110 are stopped from rotating.

If power is supplied to the solenoid 300, the movable body 320 is pulled towards the electromagnet 310 by the magnetic force of the electromagnet 310 so that the free end portion of the movable body 320 is unlocked from the locking protrusions 121 a, 122 a of the first and the second locking portions 121, 122. Accordingly, the pick-up gear 120 and the pick-up roller shaft 110 are allowed to rotate.

In the first position S3 (shown in FIGS. 2A and 6A), the movable body 320 of the solenoid 300 is locked in the locking protrusion 121 a of the first locking portion 121. Accordingly, the pick-up gear 120 and the pick-up roller 10 are stopped at the first position S3. In the second position S2 (shown in FIGS. 3A and 6B), the movable body 320 of the solenoid 300 is locked in the locking protrusion 122 a of the second locking portion 122. Accordingly the pick-up gear 120 and the pick-up roller 100 are stopped at the second position S2.

In the illustrated, exemplary embodiment, the solenoid is an armature type solenoid in which the movable body 320 is pulled to the electromagnet 310 by the magnetic force of the electromagnet 310 when power is supplied to the solenoid. The present invention is not limited to this particular type of solenoid, however, and those skilled in the art will recognize that other solenoids (such as plunger type and latch type solenoids) may also be used.

As shown in FIG. 4, a bottom tray 400 may be provided adjacent to the paper guide 130, and a plurality of papers P may be stacked on the bottom tray 400.

An end portion, adjacent to the paper guide 130, of the bottom tray 400 is elastically biased upwardly by an elastic member 410 (see FIG. 5A). The other end portion of the bottom tray 400 is pivotably hinged to the paper feeding cassette (not shown) at a pivot point 402. A pair of pressing portions 420 (such as roller-type pressing portions) are disposed at opposite sides of the bottom tray 400 to be adjacent to the pick-up roller 100 of the bottom tray 400. A pair of pick-up cams 450 are provided coaxially with the pick-up roller shaft 110 and are disposed to individually contact each of the pressing portions 420.

Each of the pick-up cams 450 is engaged with an outer circumferential surface of the pick-up roller shaft 110 and comprises a flat surface 451 and a curved surface 452.

As shown in FIGS. 5A and 5B, the pick-up cam 450 rotates coaxially with the pick-up roller shaft 110 in association with the rotation of the pick-up gear 120. The pressing portion 420, contacting the pick-up cam 450, is guided along the flat surface 451 and the curved surface 452 of the pick-up cam 450 by the rotation of the pick-up cam 450. By the guiding operation of the pressing portion 420 and the elasticity of the elastic member 410, the bottom tray 400 pivots around the pivot point 402. The pivoting operation of the bottom tray 400 presses the paper P into contact with the pick-up roller 100.

A pair of stoppers 500 are pivotably formed at an upper portion of each of the pick-up cams 450. Specifically, each of the stoppers 500 may be hinged to a frame (not shown) of the paper feeding cassette. Each of the stoppers 500 presses a portion of the curved surface 452 of the pick-up cam 450 as the pick-up cam 450 is locked in the second locking portion 122 of the pick-up gear 120 and stopped, that is, as the pick-up roller 100 stops at the second position S2.

Preferably, a locking recess 452 a is formed at one side of the curved surface 452 of the pick-up cam 450. A leading end portion of the stopper 500 is locked in the locking recess 452 a so that the pick-up cam 450 may be easily pressed.

If the pick-up roller 100 stops at the second position S2, the pick-up cam 450 is pressed by the pressing portion 420 of the bottom tray 400 to generate a moment which is opposite to the rotational direction of the pick-up roller 100, that is, a reverse moment. Therefore, the toothed portion 124 of the pick-up gear 120 interferes with the input gear 170. This interference may produce undesirable noise.

With the above-described construction, however, the stopper 500 presses the upper, curved surface 452 of the pick-up cam 450 so that the stopper absorbs some of the forces generated by the interaction of the pressing portion 420 with the pick-up cam 450. Therefore, the reverse moment of the pick-up cam 450 is attenuated, and the interference of the teeth of pick-up gear 120 and input gear 170, as well as the accompanying noise, is prevented.

The operation of the paper feeding device according to an exemplary embodiment of the present invention will now be explained in detail.

The operation of the pick-up roller 100 will be explained with reference to FIGS. 2A through 3B. As shown in FIGS. 2A and 2B, if the power supply is cut to the solenoid 300, that is, the solenoid 300 is off, the movable body 320 of the solenoid 300 of the pick-up roller 100 is locked in the first locking portion 121 of the pick-up gear 120 and the pick-up roller is stopped from rotating at the first position S3.

If power is supplied to the solenoid 300, that is, if the solenoid 300 is turned on, the pick-up roller 100 rotates, and, a sheet of paper P contacts the paper contact portion 101 and starts to be fed. The paper P is fed to the registration roller 200 until the pick-up roller 100 stops at the second position S2. Since the registration roller 200 is stopped, the paper P fed to the registration roller 200 can not pass the registration roller but forms a paper curl C (as shown in FIG. 3A) so that the leading end of the paper is registered and skew of the paper is compensated for. The paper contact portion 101 of the pick-up roller 100 still contacts the paper P, and therefore, the amount of the paper curl C can be maintained.

The registration roller 200 starts to be driven at an appropriate time, and after a certain time, the solenoid 300 is cycled on and off so that the pick-up gear 120 rotates again to the first position S3 and returns to the initial position (refer to FIGS. 2A and 2B) by the operation of the solenoid 300.

With reference to FIGS. 5A through 6B, the operation of the solenoid 300, the pick-up cam 450, and the stopper 500 according to an exemplary embodiment of the present invention will be explained. As a driving force is transmitted from a driving source (not shown) through the input gear 170 to the pick-up gear 120, the pick-up gear 120 rotates in a certain direction, such as a clockwise direction in FIGS. 5A and 5B, and the pick-up roller 100 rotates in the same direction as the pick-up gear 120.

As shown in FIG. 6A, if the power supply is cut, the leading end portion of the movable body 320 of the solenoid moves out, and the leading end is locked in the locking protrusion 121 a of the first locking portion 121 of the pick-up gear 120. At this time, the first cut off portion 125 of the pick-up gear 120 is adjacent to the input gear 170. By the first cut off portion 125, the meshed connection between the pick-up gear 120 and the input gear 170 is released so that the pick-up gear 120 and the pick-up roller 100 stop rotating.

In other words, as shown in FIG. 5A, the pick-up roller 100 stops at the first position S3 by the solenoid 300.

Under this circumstance, if power is supplied to the solenoid 300, the movable body 320 is pulled by the magnetic force of the electromagnet 310 to unlock from the locking protrusion 121 a of the first locking portion 121. Additionally, the toothed portion 124 of the pick-up gear 120 is meshed with the input gear 170 so that the pick-up gear 120 rotates and the pick-up roller 100 rotates in the same direction as the pick-up gear 120.

If the power supply is cut again to the solenoid 300, the movable body 320 is swung to the outside of the electromagnet 310 by the spring member 330 so that the leading end moves out. The leading end of the movable body 320 is guided along the guide contour 122 b of the second locking portion 122.

While being guided along the guide contour 122 b of the second locking portion 122, as shown in FIG. 6B, the leading end of the movable body 320 is locked in the locking protrusion 122 a of the second locking portion 122. At this time, the second cut off portion 126 of the pick-up gear 120 becomes adjacent to the input gear 170 and by the second cut off portion 126, the meshed connection between the pick-up gear 120 and the input gear 170 is released so that the pick-up gear 120 and the pick-up roller 100 stop rotating.

In other words, the pick-up roller 100 stops at the second position S2 by the solenoid 300, as shown in FIG. 5B.

At this time, since the registration roller 200 is stopped, the paper P fed to the registration roller 200 does not pass the registration roller 200 but forms a paper curl C so that the leading end of the paper P is registered and skew of the paper is compensated for. The paper contact portion 101 of the pick-up roller 100 still contacts the paper, and therefore, the formed curl can be maintained.

Then, if power is supplied to the solenoid 300, the movable body 320 is pulled by the magnetic force of the electromagnet 310 so as to be unlocked from the locking protrusion 122 a of the second locking portion 122. The input gear 170 meshes with the toothed portion 124 of the pick-up gear 120 to rotate and the pick-up roller 100 rotates in association with the rotation of the toothed portion 124.

If the power supply is cut to the solenoid 300, the movable body 320 swings to the outside of the electromagnet 310 by the spring member 330 so that the leading end moves out. The leading end of the movable body 320 is guided along the guide contour 121 b of the first locking portion 121.

As shown in FIGS. 5A and 5B, the pick-up cam 450 rotates coaxially with the pick-up roller shaft 110 in association with the rotation of the pick-up gear 120. The pressing portion 420, contacting the pick-up cam 450, is guided along the flat surface 451 and the curved surface 452 of the pick-up cam 450 as the pick-up cam 450 rotates. By the guiding operation of the pressing portion 420 and the elasticity of the elastic member 410, the bottom tray 400 pivots around a hinge point 402. By the pivoting operation of the bottom tray 400, the paper P is pressed to the pick-up roller 100.

If the pick-up roller 100 stops at the second position S2, the pick-up cam 450 is pressed by the pressing portion 420 of the bottom tray 400 to generate a moment in the reverse direction of the rotating direction of the pick-up roller 100, that is, a reverse moment.

The stopper 500 is pivotably formed at the upper portion of the pick-up cam 450 and presses the curved surface 452 of the pick-up cam 450. By the stopper 500, the reverse moment of the pick-up cam 450 is attenuated, and the interference of the teeth of the pick-up gear 120 with the driving gear 170, along with the associated noise, can be prevented.

As described above, the paper feeding device according to an exemplary embodiment of the present invention controls the rotation of the pick-up roller in accordance with two positions so that a paper curl can be formed and maintained to register the leading end of a sheet of paper and compensate for skew of the paper, without requiring a feeding roller.

Additionally, the paper feeding device according to an exemplary embodiment of the present invention prevents tooth interference and the accompanying noise so that the paper feeding device operates with enhanced stability and precision.

While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 

1. A paper feeding device for an image forming apparatus, comprising: a pick-up roller with a paper contact portion; a registration roller for registering a leading end of a paper fed by the pick-up roller and compensating for skew of the paper; and a driving unit to drive the pick-up roller between a first position for preparing to pick up a sheet of paper and a second position for forming a paper curl.
 2. The device as claimed in claim 1, the driving unit comprising: a pick-up gear engaged with a pick-up roller shaft; and a solenoid engaging the pickup gear, the solenoid stopping the pick-up gear from rotating at each of the first and the second positions.
 3. The device as claimed in claim 2, wherein the pick-up gear comprises first and second locking portions corresponding to each of the first and the second positions; and the solenoid comprises a movable body which may be locked in the first and the second locking portions so that the pick-up gear is stopped at the first and the second positions, respectively.
 4. The device as claimed in claim 3, wherein each of the first and the second locking portions comprises a locking protrusion at one side, and a guide contour at the other side.
 5. The device as claimed in claim 1, wherein a rotational distance of the pick-up roller is set to meet the following equation: 1+α≦<L<LE in which, L is the distance the pick-up roller rotates from a reference position (S1) where the paper contact portion of the pick-up roller starts to contact the paper to the second position (S2), 1 is a distance between the reference position (S1) and the registration roller, α is an amount of paper curl, and LE is a distance between the reference position (S1) and the first position (S3).
 6. The device as claimed in claim 1, further comprising: a bottom tray for pressing the paper into contact with the pick-up roller; and means for preventing a reverse moment which is generated at the pick-up roller by the bottom tray.
 7. The device as claimed in claim 6, wherein the means for preventing the reverse moment comprises: a pick-up cam rotating coaxially with the pick-up roller to move the bottom tray upwardly and downwardly; and a cam stopper pressing the pick-up cam to prevent the reverse moment generated by the bottom tray.
 8. The device as claimed in claim 7, wherein the pick-up cam comprises a locking recess in which a leading end of the cam stopper is locked.
 9. A paper feeding device for an image forming apparatus comprising: a registration roller for registering a leading end of a sheet of paper and compensating for skew of the paper; and a pick-up roller for picking up a sheet of paper to feed to the registration roller and, as the leading end of the sheet of paper contacts the registration roller to form a certain paper curl, stopping to maintain the paper curl.
 10. The device as claimed in claim 9, further comprising: a solenoid controlling the rotation of the pick-up roller to stop the pick-up roller at a first position for preparing to pick-up a sheet of paper and at a second position for forming a paper curl.
 11. The device as claimed in claim 10, further comprising: a pick-up roller shaft rotatably supporting the pick-up roller; a pick-up gear engaged with the pick-up roller shaft to rotate the pick-up roller, wherein the pick-up gear comprises a first and a second locking portions corresponding to the first and the second positions, and wherein the solenoid comprises a movable body which may be locked in the first and the second locking portions so that the pick-up gear is stopped at the first and the second positions, respectively.
 12. The device as claimed in claim 11, wherein each of the first and the second locking portions comprises a locking protrusion at one side, and a guide contour at the other side.
 13. The device as claimed in claim 10, wherein a rotational distance of the pick-up roller is set to meet the following equation: 1+α≦L<LE in which, L is the distance the pick-up roller rotates from a reference position (S1) where the paper contact portion of the pick-up roller starts to contact the paper to the second position (S2), 1 is a distance between the reference position (S1) and the registration roller, α is an amount of paper curl, and LE is a distance between the reference position (S1) and the first position (S3).
 14. The device as claimed in claim 9, further comprising: a bottom tray for pressing the paper into contact with the pick-up roller; and means for preventing a reverse moment which is generated at the pick-up roller by the bottom tray.
 15. The device as claimed in claim 14, wherein the means for preventing the reverse moment comprises: a pick-up cam rotating coaxially with the pick-up roller to move the bottom tray upwardly and downwardly; and a cam stopper pressing the pick-up cam to prevent the reverse moment generated by the bottom tray.
 16. The device as claimed in claim 15, wherein the pick-up cam comprises a locking recess in which a leading end of the cam stopper is locked.
 17. A paper feeding device for an image forming apparatus, comprising: a registration roller for registering a leading end of a sheet of paper; a rotatable pick-up roller for picking up a sheet of paper from a stack of paper and feeding the sheet of paper to the registration roller, the pick-up roller having a paper contact portion; means for rotating the pick-up roller and stopping the pick-up roller at a first stop position and a second stop position, wherein the first stop position and the second stop position are arranged to meet the following equation: 1+α≦L<LE in which, L is the distance the pick-up roller rotates from a reference position (S1) where the paper contact portion of the pick-up roller starts to contact the paper to the second stop position (S2), 1 is a distance between the reference position (S1) and the registration roller, α is an amount of paper curl, and LE is a distance between the reference position (S1) and the first stop position (S3).
 18. The device as claimed in claim 17, wherein the means for rotating and stopping the pick-up roller comprises: a rotatable pick-up roller gear engaging the pick-up roller, the pick-up roller gear being driven to rotate the pick-up roller, the pick-up roller gear having first and second locking portions; and means for engaging the first and second locking portions of the pick-up roller gear to prevent the pick-up roller gear from rotating.
 19. The device as claimed in claim 18, wherein the means for engaging the first and second locking portions of the pick-up roller gear comprises: a solenoid engaging the pickup gear.
 20. The device as claimed in claim 18, wherein the pick-up roller gear is driven by an input gear, and the pick-up roller gear has a toothed portion where the pick-up roller gear is engaged with the input gear, and has first and second cut-off portions where the pick-up roller gear is not engaged with the input gear, the first and second cut-off portions corresponding to the first and second stop positions. 